Novel ester compounds, polymers, resist compositions and patterning process

ABSTRACT

An ester compound of the following formula (1) is provided.  
                 
 
     R 1  is H, methyl or CH 2 CO 2 R 3 , R 2  is H, methyl or CO 2 R 3 , R 3  is C 1 -C 15  alkyl, k is 0 or 1, Z is a divalent C 2 -C 20  hydrocarbon group which forms a single ring or bridged ring with the carbon atom and which may contain a hetero atom, m is 0 or 1, n is 0, 1, 2 or 3, and 2m+n=2 or 3. A resist composition comprising as the base resin a polymer resulting from the ester compound is sensitive to high-energy radiation, has excellent sensitivity, resolution, and etching resistance, and is suited for micropatterning using electron beams or deep-UV.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to (1) a novel ester compound, (2)a polymer comprising units of the ester compound which is blended as abase resin to formulate a resist composition having a high sensitivity,resolution and etching resistance, and in particular, suitable asmicropatterning material for VLSI fabrication, (3) a method forpreparing the polymer, (4) a resist composition comprising the polymer,and (5) a patterning process using the resist composition.

[0003] 2. Prior Art

[0004] While a number of recent efforts are being made to achieve afiner pattern rule in the drive for higher integration and operatingspeeds in LSI devices, deep-ultraviolet lithography is thought to holdparticular promise as the next generation in microfabricationtechnology. In particular, photolithography using a KrF or ArF excimerlaser as the light source is strongly desired to reach the practicallevel as the micropatterning technique capable of achieving a featuresize of 0.3 μm or less.

[0005] For resist materials for use with a KrF excimer lasers,polyhydroxystyrene having a practical level of transmittance and etchingresistance is, in fact, a standard base resin. For resist materials foruse with ArF excimer lasers, polyacrylic or polymethacrylic acidderivatives and polymers comprising aliphatic cyclic compounds in thebackbone are under investigation. In either case, the basic concept isthat some or all of alkali soluble sites of alkali soluble resin areprotected with acid labile or eliminatable groups. The overallperformance of resist material is adjusted by a choice from among avariety of acid eliminatable protective groups.

[0006] Exemplary acid eliminatable protective groups includetert-butoxycarbonyl (JP-B 2-27660), tert-butyl (JP-A 62-115440, JP-A5-80515, and J. Photopolym. Sci. Technol. 7 [3], 507 (1994)),2-tetrahydropyranyl (JP-A 2-19847, 5-80515 and 5-88367), and1-ethoxyethyl (JP-A 2-19847 and 4-215661). While it is desired toachieve a finer pattern rule, none of these acid eliminatable protectivegroups are deemed to exert satisfactory performance.

[0007] More particularly, tert-butoxycarbonyl and tert-butyl areextremely less reactive with acids so that a substantial quantity ofenergy radiation must be irradiated to generate a sufficient amount ofacid in order to establish a difference in rate of dissolution beforeand after exposure. If a photoacid generator of the strong acid type isused, the exposure can be reduced to a relatively low level becausereaction can proceed with a small amount of acid generated. However, inthis event, the deactivation of the generated acid by air-borne basicsubstances has a relatively large influence, giving rise to suchproblems as a T-top pattern. On the other hand, 2-tetrahydropyranyl and1-ethoxyethyl are so reactive with acids that with the acid generated byexposure, elimination reaction may randomly proceed without a need forheat treatment, with the result that substantial dimensional changesoccur between exposure and heat treatment/development. Where thesegroups are used as protective groups for carboxylic acid, they have alow dissolution inhibiting effect to alkali, resulting in a high rate ofdissolution in unexposed areas and film thinning during development. Ifhighly substituted polymers are used to avoid such inconvenience, thereresults an extreme drop of heat resistance. These resins fail to providea difference in rate of dissolution before and after exposure, resultingin resist materials having a very low resolution.

SUMMARY OF THE INVENTION

[0008] Therefore, an object of the present invention is to provide (1) anovel ester compound capable of forming an acid-decomposable polymer,(2) a polymer which is blended as a base resin to formulate a resistcomposition having a higher sensitivity, resolution and etchingresistance than conventional resist compositions, (3) a method forpreparing the polymer, (4) a resist composition comprising the polymeras a base resin, and (5) a patterning process using the resistcomposition.

[0009] The inventor has found that a novel ester compound of thefollowing general formula (1) obtained by the method to be describedlater is useful in preparing an acid-decomposable polymer; that a resistcomposition comprising as the base resin a novel polymer prepared fromthe ester compound to a weight average molecular weight of 1,000 to500,000 has a high sensitivity, resolution and etching resistance; andthat this resist composition lends itself to precise micropatterning.

[0010] In a first aspect, the invention provides an ester compound ofthe following general formula (1).

[0011] Herein R¹ is hydrogen, methyl or CH₂CO₂R³, R² is hydrogen, methylor CO₂R³, R³ is a straight, branched or cyclic alkyl group of 1 to 15carbon atoms, k is 0 or 1, Z is a divalent hydrocarbon group of 2 to 20carbon atoms which forms a single ring or bridged ring with the carbonatom and which may contain a hetero atom, m is 0 or 1, n is 0, 1, 2 or3, and 2m+n is 2 or 3.

[0012] In a second aspect, the invention provides a polymer comprisingrecurring units of the following general formula (1a-1) and/or (1a-2)derived from an ester compound of the general formula (1), and having aweight average molecular weight of 1,000 to 500,000.

[0013] (1a-1) (1a-2)

[0014] Herein R¹, R², Z, k, m and n are as defined above.

[0015] In a preferred embodiment, the polymer further comprisesrecurring units of at least one of the following formulas (2a) to (10a).

[0016] Herein R¹, R² and k are as defined above; R⁴ is hydrogen or acarboxyl or hydroxyl-containing monovalent hydrocarbon group of 1 to 15carbon atoms; at least one of R⁵ to R⁸ is a carboxyl orhydroxyl-containing monovalent hydrocarbon group of 1 to 15 carbonatoms, and the remainders are independently hydrogen or a straight,branched or cyclic alkyl group of 1 to 15 carbon atoms, or R⁵ to R⁸,taken together, may form a ring, and when they form a ring, at least oneof R⁵ to R⁸ is a carboxyl or hydroxyl-containing divalent hydrocarbongroup of 1 to 15 carbon atoms, and the remainders are independently asingle bond or a straight, branched or cyclic alkylene group of 1 to 15carbon atoms; R⁹ is a monovalent hydrocarbon group of 3 to 15 carbonatoms containing a —CO₂— partial structure; at least one of R¹⁰ to R¹³is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a—CO₂— partial structure, and the remainders are independently hydrogenor a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms,or R¹⁰ to R¹³, taken together, may form a ring, and when they form aring, at least one of R¹⁰ to R¹³ is a divalent hydrocarbon group of 1 to15 carbon atoms containing a —CO₂— partial structure, and the remaindersare independently a single bond or a straight, branched or cyclicalkylene group of 1 to 15 carbon atoms; R¹⁴ is a polycyclic hydrocarbongroup of 7 to carbon atoms or an alkyl group containing such apolycyclic hydrocarbon group; R¹⁵ is an acid labile group; X is —CH₂— or—O—; and Y is —O— or —(NR¹⁶)— wherein R¹⁶ is hydrogen or a straight,branched or cyclic alkyl group of 1 to 15 carbon atoms.

[0017] In a third aspect, the invention provides a method for preparinga polymer comprising the step of effecting radical polymerization,anionic polymerization or coordination polymerization between an estercompound of the general formula (1) and another compound having acarbon-to-carbon double bond.

[0018] In a fourth aspect, the invention provides a resist compositioncomprising the polymer defined above, and more specifically, a resistcomposition comprising the polymer defined above, a photoacid generator,and an organic solvent.

[0019] In a fifth aspect, the invention provides a process for forming aresist pattern comprising the steps of applying the resist compositiondefined above onto a substrate to form a coating; heat treating thecoating and then exposing it to high-energy radiation or electron beamsthrough a photo mask; and optionally heat treating the exposed coatingand developing it with a developer.

[0020] The ester compound of formula (1) and the polymer comprisingunits of formula (1a-1) and/or (1a-2) employ a cycloalkylcycloalkyl orcycloalkylcycloalkenyl group of the following formula (1b) as theacid-eliminatable protective group, thereby overcoming the drawbacks ofthe tert-butoxycarbonyl and tert-butyl groups having low reactivity withacid as well as the 2-tetrahydropyranyl and 1-ethoxyethyl groups havingtoo high reactivity with acid and low resistance to alkaline developers.

[0021] Herein, Z, m and n are as defined above, the broken line denotesa valence bond.

[0022] The ester compound of formula (1) is decomposed under acidicconditions while generating an olefin compound and a carboxylic acid.This mechanism itself is apparently identical with the decomposition oftertiary alkyl esters such as tert-butyl esters although thedecomposition rate significantly differs between them. In the acidolysisof a tertiary alkyl ester, carboxylic acid and a tertiary alkyl cationgenerate first, then the extinction of the cation due to proton releaseoccurs to form an olefin compound, whereby the reaction comes to an end.The rate-determining stage of this decomposition reaction is the latestage of cation extinction. The progress of this stage is very rapid inthe case of the ester compound of formula (1), probably because themoderated distortion of the ring and the formation of a conjugatedsystem produce a strong thrust. The olefin compound produced has a verylow re-reactivity. As a consequence, the ester compound of formula (1)provides a high degree of acidolysis surpassing other tertiary alkylesters.

[0023] Since the ester compound of formula (1) is basically a tertiaryalkyl ester, it, when formulated into a resist composition, does notallow for the infinite progress of decomposition in a duration betweenexposure and development and film thinning during development as foundwith 2-tetrahydropyranyl and 1-ethoxyethyl. When a polymer comprisingconstituent units derived from the compound is formulated as the baseresin, there is obtained a resist composition which possesses a highsensitivity and resolution and has a high dissolution contrast in thatthe unexposed areas have a very slow rate of dissolution while the areashaving undergone an adequate dose of exposure quickly become alkalisoluble. Additionally, very high etching resistance is exerted by virtueof the robust aliphatic ring positioned on the backbone of the polymerand a plurality of aliphatic rings contained in the protective group offormula (1b).

BRIEF DESCRIPTION OF THE DRAWING

[0024] The only figure, FIG. 1 is a diagram showing the ¹H-NMR spectrumof the monomer obtained in Synthesis Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] Ester Compound

[0026] The novel ester compounds according to the first aspect of theinvention are of the following general formula (1) .

[0027] Herein, R¹ is hydrogen, methyl or CH₂Co₂R³. R² is hydrogen,methyl or CO₂R³. R³ stands for straight, branched or cyclic alkyl groupsof 1 to 15 carbon atoms, such as, for example, methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl,ethylcyclohexyl, butylcyclohexyl, adamantyl, ethyladamantyl andbutyladamantyl.

[0028] Z is a divalent hydrocarbon group of 2 to 20 carbon atoms whichforms a single ring or bridged ring with the carbon atom and which maycontain a hetero atom, for example, single ring-forming hydrocarbongroups such as cyclopropane, cyclobutane, cyclopentane, cyclohexane,cycloheptane, and cyclooctane; bridged ring-forming hydrocarbon groupssuch as bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane,bicyclo[4.4.0]decane and tricyclo[5.2.1.0^(2,6)]decane; and ring-forminghydrocarbon groups in which some of the hydrogen atoms in the foregoinggroups are substituted with alkyl, hydroxy, alkoxy, acyloxy,alkylcarbonyl, hydroxycarbonyl, alkoxycarbonyl and oxo, among others.

[0029] The letter k is 0 or 1, m is 0 or 1, n is 0, 1, 2 or 3, and 2m+nis equal to 2 or 3.

[0030] Illustrative, non-limiting, examples of the ester compounds ofthe invention are given below.

[0031] The ester compound of the invention is prepared, for example, bythe following process, although the preparation is not limited thereto.

[0032] Herein, R¹, R², Z, k, m and n are as defined above, and Hal isbromine or chlorine.

[0033] Step A is to effect nucleophilic addition reaction with thecarbonyl on a cyclic ketone compound to form a tertiary alcohol. Thisstage is typified by Grignard reaction, but not limited thereto.Reaction readily takes place under well-known conditions, preferably bymixing the reactants: cyclic ketone compound, alkyl halide and magnesiumin a solvent such as tetrahydrofuran or diethyl ether, while heating orcooling the reaction mixture if desired.

[0034] Step B is to convert the tertiary alcohol to an ester ofunsaturated acid. Reaction readily takes place under well-knownconditions, preferably by mixing the reactants: tertiary alcohol,unsaturated carboxylic halide (e.g., acrylic chloride or methacrylicchloride) and base (e.g., triethylamine) in a solvent such as methylenechloride, while cooling the reaction mixture if desired.

[0035] Step C is to construct an alicyclic skeleton through Diels-Alderreaction. Reaction readily takes place under well-known conditions,preferably by mixing the reactants: ester of unsaturated acid andcyclopentadiene in a solventless system or in a solvent such as benzene,optionally in the presence of a catalyst such as boron trifluoride,while heating or cooling the reaction mixture if desired.

[0036] Polymer

[0037] In the second aspect, the invention provides a polymer or highmolecular weight compound comprising recurring units of the followinggeneral formula (1a-1) and/or (1a-2) derived from an ester compound ofthe general formula (1), and having a weight average molecular weight of1,000 to 500,000, and preferably 5,000 to 100,000.

[0038] Herein R¹, R², Z, k, m and n are as defined above.

[0039] The polymer of the invention may further comprise recurring unitsof at least one type selected from recurring units of the followingformulas (2a) to (10a) which are derived from monomers of the followinggeneral formulas (2) to (10).

[0040] In the above formulae, X is —CH₂— or —O—; Y is —O— or —(NR¹⁶)-wherein R¹⁶ is hydrogen or a straight, branched or cyclic alkyl group of1 to 15 carbon atoms; and k is equal to 0 or 1. Then formulae (6a-1) to(9a-2) may also be represented by the following formulae (6a-1-1) to(9a-2-2).

[0041] Herein R¹ and R² are as defined above.

[0042] R⁴ stands for hydrogen or carboxyl or hydroxyl-containingmonovalent hydrocarbon groups of 1 to 15 carbon atoms, for example,carboxyethyl, carboxybutyl, carboxycyclopentyl, carboxycyclohexyl,carboxynorbornyl, carboxyadamantyl, hydroxyethyl, hydroxybutyl,hydroxycyclopentyl, hydroxycyclohexyl, hydroxynorbornyl, andhydroxyadamantyl.

[0043] At least one of R⁵ to R⁸ is a carboxyl or hydroxyl-containingmonovalent hydrocarbon group of 1 to 15 carbon atoms, and the remainingR's are independently hydrogen or a straight, branched or cyclic alkylgroup of 1 to 15 carbon atoms. Examples of the carboxyl orhydroxyl-bearing monovalent hydrocarbon group of 1 to 15 carbon atomsinclude carboxy, carboxymethyl, carboxyethyl, carboxybutyl,hydroxymethyl, hydroxyethyl, hydroxybutyl, 2-carboxy-ethoxycarbonyl,4-carboxybutoxycarbonyl, 2-hydroxyethoxy-carbonyl,4-hydroxybutoxycarbonyl, carboxycyclopentyl-oxycarbonyl,carboxycyclohexyloxycarbonyl, carboxynorbornyl-oxycaronyl,carboxyadamantyloxycarbonyl, hydroxy-cyclopentyloxycarbonyl,hydroxycyclohexyloxycarbonyl, hydroxynorbornyloxycarbonyl, andhydroxyadamantyloxy-carbonyl. Examples of the straight, branched orcyclic alkyl group of 1 to 15 carbon atoms are the same as exemplifiedfor R³ . R⁵ to R⁸, taken together, may form a ring, and in that event,at least one of R⁵ to R⁸ is a divalent hydrocarbon group of 1 to 15carbon atoms having a carboxyl or hydroxyl group, while the remainingR's are independently single bonds or straight, branched or cyclicalkylene groups of 1 to 15 carbon atoms. Examples of the carboxyl orhydroxyl-bearing divalent hydrocarbon group of 1 to 15 carbon atomsinclude the groups exemplified as the carboxyl or hydroxyl-bearingmonovalent hydrocarbon group, with one hydrogen atom eliminatedtherefrom. Examples of the straight, branched or cyclic alkylene groupsof 1 to 15 carbon atoms include the groups exemplified for R³, with onehydrogen atom eliminated therefrom.

[0044] R⁹ is a monovalent hydrocarbon group of 3 to 15 carbon atomscontaining a —CO₂— partial structure, for example, 2-oxooxolan-3-yl,4,4-dimethyl-2-oxooxolan-3-yl, 4-methyl-2-oxooxan-4-yl,2-oxo-1,3-dioxolan-4-ylmethyl, and 5-methyl-2-oxooxolan-5-yl. At leastone of R¹⁰ to R¹³ is a monovalent hydrocarbon group of 2 to 15 carbonatoms containing a —CO₂— partial structure, while the remaining R's areindependently hydrogen or straight, branched or cyclic alkyl groups of 1to 15 carbon atoms. Examples of the monovalent hydrocarbon group of 2 to15 carbon atoms containing a —CO₂— partial structure include2-oxooxolan-3-yloxycarbonyl, 4,4-dimethyl-2-oxooxolan-3-yloxycarbonyl,4-methyl-2-oxooxan-4-yloxycarbonyl,2-oxo-1,3-dioxolan-4-ylmethyloxycarbonyl, and5-methyl-2-oxooxolan-5-yloxycarbonyl. Examples of the straight, branchedor cyclic alkyl groups of 1 to 15 carbon atoms are the same asexemplified for R³. R¹⁰ to R¹³, taken together, may form a ring, and inthat event, at least one of R¹⁰ to R¹³ is a divalent hydrocarbon groupof 1 to 15 carbon atoms containing a —CO₂— partial structure, while theremaining R's are independently single bonds or straight, branched orcyclic alkylene groups of 1 to 15 carbon atoms. Examples of the divalenthydrocarbon group of 1 to 15 carbon atoms containing a —CO₂— partialstructure include 1-oxo-2-oxapropane-1,3-diyl,1,3-dioxo-2-oxapropane-1,3-diyl, 1-oxo-2-oxabutane-1,4-diyl, and1,3-dioxo-2-oxabutane-1,4-diyl, as well as the groups exemplified as themonovalent hydrocarbon group containing a —CO₂— partial structure, withone hydrogen atom eliminated therefrom. Examples of the straight,branched or cyclic alkylene groups of 1 to 15 carbon atoms include thegroups exemplified for R³ ₁ with one hydrogen atom eliminated therefrom.

[0045] R¹⁴ is a polycyclic hydrocarbon group having 7 to 15 carbon atomsor an alkyl group containing a polycyclic hydrocarbon group, forexample, norbornyl, bicyclo[3.3.1]-nonyl, tricyclo[5.2.1.0.^(2,6)]decyl,adamantyl, ethyladamantyl, butyladamantyl, norbornylmethyl, andadamantylmethyl.

[0046] R¹⁵ is an acid labile group, and k is 0 or 1.

[0047] X is —CH₂— or —O—.

[0048] Y is —O— or —(NR¹⁶)- wherein R¹⁶ is hydrogen or a straight,branched or cyclic alkyl group of 1 to 15 carbon atoms, examples ofwhich are as described for R³.

[0049] The acid labile groups represented by R¹⁵ may be selected from avariety of such groups. Examples of the acid labile group are groups ofthe following general formulae (L1) to (L4), tertiary alkyl groups of 4to 20 carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilylgroups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkylgroups of 4 to 20 carbon atoms.

[0050] R^(L01) and R^(L02) are hydrogen or straight, branched or cyclicalkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms.Exemplary alkyl groups include methyl, ethyl, propyl, isopropyl,n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl,and n-octyl. R^(L03) is a monovalent hydrocarbon group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms, which may contain a hetero atomsuch as oxygen, examples of which include unsubstituted straight,branched or cyclic alkyl groups and straight, branched or cyclic alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples are thesubstituted alkyl groups shown below.

[0051] A pair of R^(L01) and R^(L02), R^(L01) and R^(L03), or R^(L02)and R^(L03) may form a ring. Each of R^(L01), R^(L02) and R^(L03) is astraight or branched alkylene group of 1 to 18 carbon atoms, preferably1 to 10 carbon atoms when they form a ring.

[0052] R^(L04) is a tertiary alkyl group of 4 to 20 carbon atoms,preferably 4 to 15 carbon atoms, a trialkylsilyl group in which eachalkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (L1). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-5-oxooxolan-4-yl. Letter y is an integer of 0 to 6.

[0053] R^(L05) is a straight or branched alkyl group of 1 to 8 carbonatoms or a substituted or unsubstituted aryl group of 6 to 20 carbonatoms. Examples of the straight, branched or cyclic alkyl group includemethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-amyl, n-pentyl and n-hexyl. Exemplary aryl groups are phenyl,methylphenyl, naphthyl, anthryl, phenanthryl, and pyrenyl. Letter m isequal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or3.

[0054] R^(L06) is a straight, branched or cyclic alkyl group of 1 to 8carbon atoms or a substituted or unsubstituted aryl group of 6 to 20carbon atoms. Examples of these groups are the same as exemplified forR^(L05).

[0055] R^(L07) to R^(L16) independently represent hydrogen or monovalenthydrocarbon groups of 1 to 15 carbon atoms which may contain a heteroatom. Exemplary hydrocarbon groups are straight, branched or cyclicalkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-octyl, n-nonyl,n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl and cyclohexylbutyl,and substituted ones of these groups in which some hydrogen atoms arereplaced by hydroxyl, alkoxy, carboxy, alkoxycarbonyl, oxo, amino,alkylamino, cyano, mercapto, alkylthio, sulfo or other groups.Alternatively, R^(L07) to R^(L16), taken together, form a ring (forexample, a pair of R^(L07) and R^(L08), R^(L07) and R^(L09), R^(L08) andR^(L10), R^(L09) and R^(L10), R^(L11) and R^(L12), R^(L13) and R^(L14),or a similar pair form a ring). Each of R^(L07) to R^(L16) represents adivalent C₁-C₁₅ hydrocarbon group which may contain a hetero atom, whenthey form a ring, examples of which are the ones exemplified above forthe monovalent hydrocarbon groups, with one hydrogen atom beingeliminated. Two of R^(L07) to R^(L16) which are attached to adjoiningcarbon atoms (for example, a pair of R^(L07) and R^(L09), R^(L09) andR^(L15), R^(L13) and R^(L15), or a similar pair) may bond togetherdirectly to form a double bond.

[0056] Of the acid labile groups of formula (L1), the straight andbranched ones are exemplified by the following groups.

[0057] Of the acid labile groups of formula (L1), the cyclic ones are,for example, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

[0058] Examples of the acid labile groups of formula (L2) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyl-oxycarbonylmethyl,1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxy-carbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

[0059] Examples of the acid labile groups of formula (L3) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butyl-cyclopentyl, 1-sec-butylcyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl groups.

[0060] The acid labile groups of formula (L4) are exemplified by thefollowing groups.

[0061] The polymer of the invention may be prepared by polymerizing anester compound of formula (1) or by copolymerizing a first monomer inthe form of an ester compound of formula (1) with a second monomer inthe form of at least one compound of formulas (2) to (10). By properlyadjusting the proportion of the respective monomers used in a thecopolymerization reaction, the polymer can be tailored so that it mayexert the preferred performance when blended in resist compositions.

[0062] In addition to (i) the monomer of formula (1) and (ii) themonomer or monomers of formulas (2) to (10), the polymer of theinvention may have copolymerized therewith (iii) another monomer havinga carbon-to-carbon double bond other than (i) and (ii). Examples of theadditional monomer (iii) include substituted acrylic acid esters such asmethyl methacrylate, methyl crotonate, dimethyl maleate, and dimethylitaconate, unsaturated carboxylic acids such as maleic acid, fumaricacid and itaconic acid, substituted or unsubstituted norbornenes such asnorbornene and methyl norbornene-5-carboxylate, and unsaturated acidanhydrides such as itaconic anhydride.

[0063] The polymers of the invention may contain

[0064] (I) more than 0 mol % to 100 mol %, preferably 20 to 90 mol %,more preferably 30 to 80 mol % of units of formula (1a-1) and/or (1a-2)derived from the monomer of formula (1),

[0065] (II) 0 mol % to less than 100 mol %, preferably 1 to 95 mol %,more preferably 5 to 90 mol % of units of one or more types of formulae(2a) to (10a) derived from the monomers of formulae (2) to (10), andoptionally,

[0066] (III) 0 to 80 mol %, preferably 0 to 70 mol %, more preferably 0to 50 mol % of units of one or more types derived from the additionalmonomers (iii).

[0067] The polymers of the invention have a weight average molecularweight of 1,000 to 500,000, preferably 3,000 to 100,000. Outside therange, the etching resistance may become extremely low and theresolution may become low because a substantial difference in rate ofdissolution before and after exposure is lost.

[0068] In the method according to the third aspect of the invention, apolymer is prepared by effecting radical polymerization, anionicpolymerization or coordination polymerization between an ester compoundof formula (1) and another compound having a carbon-to-carbon doublebond, which is typically selected from the above-described monomers (ii)and (iii).

[0069] For radical polymerization, preferred reaction conditions include(a) a solvent selected from among hydrocarbons such as benzene, etherssuch as tetrahydrofuran, alcohols such as ethanol, and ketones such asmethyl isobutyl ketone, (b) a polymerization initiator selected from azocompounds such as 2,2′-azobisisobutyronitrile and peroxides such asbenzoyl peroxide and lauroyl peroxide, (c) a temperature of about 0° C.to about 100° C., and (d) a time of about ½ hour to about 48 hours.Reaction conditions outside the described range may be employed ifdesired.

[0070] For anionic polymerization, preferred reaction conditions include(a) a solvent selected from among hydrocarbons such as benzene, etherssuch as tetrahydrofuran, and liquid ammonia, (b) a polymerizationinitiator selected from metals such as sodium and potassium, alkylmetals such as n-butyllithium and sec-butyllithium, ketyl, and Grignardreagents, (c) a temperature of about −78° C. to about 0° C., (d) a timeof about ½ hour to about 48 hours, and (e) a stopper selected from amongproton-donative compounds such as methanol, halides such as methyliodide, and electrophilic compounds. Reaction conditions outside thedescribed range may be employed if desired.

[0071] For coordination polymerization, preferred reaction conditionsinclude (a) a solvent selected from among hydrocarbons such as n-heptaneand toluene, (b) a catalyst selected from Ziegler-Natta catalystscomprising a transition metal (e.g., titanium) and alkylaluminum,Phillips catalysts of metal oxides having chromium or nickel compoundscarried thereon, and olefin-metathesis mixed catalysts as typified bytungsten and rhenium mixed catalysts, (c) a temperature of about 0° C.to about 100° C., and (d) a time of about ½ hour to about 48 hours.Reaction conditions outside the described range may be employed ifdesired.

[0072] Resist Composition

[0073] Since the polymer of the invention is useful as the base polymerof a resist composition, the other aspect of the invention provides aresist composition comprising the polymer. Specifically, the resistcomposition is defined as comprising the polymer, a photoacid generator,and an organic solvent.

[0074] Photoacid Generator

[0075] The photoacid generator is a compound capable of generating anacid upon exposure to high energy radiation or electron beams andincludes the following:

[0076] (i) onium salts of the formula (P1a-1), (P1a-2) or (P1b),

[0077] (ii) diazomethane derivatives of the formula (P2),

[0078] (iii) glyoxime derivatives of the formula (P3),

[0079] (iv) bissulfone derivatives of the formula (P4),

[0080] (v) sulfonic acid esters of N-hydroxyimide compounds of theformula (P5),

[0081] (vi) P-ketosulfonic acid derivatives,

[0082] (vii) disulfone derivatives,

[0083] (viii) nitrobenzylsulfonate derivatives, and

[0084] (ix) sulfonate derivatives.

[0085] These photoacid generators are described in detail.

[0086] (i) Onium salts of formula (P1a-1), (P1a-2) or (P1b):

[0087] Herein, R^(101a), R^(101b), and R^(101c) independently representstraight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenylgroups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, oraralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some orall of the hydrogen atoms may be replaced by alkoxy or other groups.Also, R^(101b) and R^(101c), taken together, may form a ring. R^(101b)and R^(101c) each are alkylene groups of 1 to 6 carbon atoms when theyform a ring. K- is a non-nucleophilic counter ion.

[0088] R^(101a), R^(101b), and R^(101c) may be the same or different andare illustrated below. Exemplary alkyl groups include methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl,heptyl, octyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl,4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl.Exemplary alkenyl groups include vinyl, allyl, propenyl, butenyl,hexenyl, and cyclohexenyl. Exemplary oxoalkyl groups include2-oxocyclopentyl and 2-oxocyclohexyl as well as 2-oxopropyl,2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and2-(4-methylcyclohexyl)-2-oxoethyl. Exemplary aryl groups include phenyland naphthyl; alkoxyphenyl groups such as p-methoxyphenyl,m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, andm-tert-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl,4-butylphenyl, and dimethylphenyl; alkylnaphthyl groups such asmethylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such asmethoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such asdimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups suchas dimethoxynaphthyl and diethoxynaphthyl. Exemplary aralkyl groupsinclude benzyl, phenylethyl, and phenethyl. Exemplary aryloxoalkylgroups are 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl,2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl. Examples ofthe non-nucleophilic counter ion represented by K⁻ include halide ionssuch as chloride and bromide ions, fluoroalkylsulfonate ions such astriflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate,arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzene-sulfonate,and alkylsulfonate ions such as mesylate and butanesulfonate.

[0089] Herein, R^(102a) and R^(102b) independently represent straight,branched or cyclic alkyl groups of 1 to 8 carbon atoms. R¹⁰³ representsa straight, branched or cyclic alkylene groups of 1 to 10 carbon atoms.R^(104a) and R^(104b) independently represent 2-oxoalkyl groups of 3 to7 carbon atoms. K⁻ is a non-nucleophilic counter ion.

[0090] Illustrative of the groups represented by R^(102a) and R^(102b)are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, and cyclohexylmethyl.Illustrative of the groups represented by R^(L03) are methylene,ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene,nonylene, 1,4-cyclohexylene, 1,2-cyclohexylene, 1,3-cyclopentylene,1,4-cyclooctylene, and 1,4-cyclohexanedimethylene. Illustrative of thegroups represented by R^(104a) and R^(104b) are 2-oxopropyl,2-oxocyclopentyl, 2-oxocyclohexyl, and 2-oxocycloheptyl. Illustrativeexamples of the counter ion represented by K⁻ are the same asexemplified for formulae (P1a-1) and (P1a-2).

[0091] (ii) Diazomethane derivatives of formula (P2)

[0092] Herein, R¹⁰⁵ and R¹⁰⁶ independently represent straight, branchedor cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms,aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkylgroups of 7 to 12 carbon atoms.

[0093] Of the groups represented by R¹⁰⁵ and R¹⁰⁶, exemplary alkylgroups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, pentyl, hexyl, heptyl, octyl, amyl, cyclopentyl, cyclohexyl,cycloheptyl, norbornyl, and adamantyl. Exemplary halogenated alkylgroups include trifluoromethyl, 1,1,1-trifluoroethyl,1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups includephenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl,o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, andm-tert-butoxyphenyl; and alkylphenyl groups such as 2-methyl-phenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl,4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groupsinclude fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl.Exemplary aralkyl groups include benzyl and phenethyl.

[0094] (iii) Glyoxime derivatives of formula (P3)

[0095] Herein, R¹⁰⁷, R¹⁰⁸, and R¹⁰⁹ independently represent straight,branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbonatoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, oraralkyl groups of 7 to 12 carbon atoms. Also, R¹⁰⁸ and R¹⁰⁹, takentogether, may form a ring. R¹⁰⁸ and R¹⁰⁹ each are straight or branchedalkylene groups of 1 to 6 carbon atoms when they form a ring.

[0096] Illustrative examples of the alkyl, halogenated alkyl, aryl,halogenated aryl, and aralkyl groups represented by R¹⁰⁷, R¹⁰⁸, and R¹⁰⁹are the same as exemplified for R¹⁰⁵ and R¹⁰⁶. Examples of the alkylenegroups represented by R¹⁰⁸ and R¹⁰⁹ include methylene, ethylene,propylene, butylene, and hexylene.

[0097] (iv) Bissulfone derivatives of formula (P4)

[0098] Herein, R^(101a) and R^(101b) are as defined above.

[0099] (v) Sulfonic acid esters of N-hydroxyimide compounds of formula(P5)

[0100] Herein, R¹¹⁰ is an arylene group of 6 to 10 carbon atoms,alkylene group of 1 to 6 carbon atoms, or alkenylene group of 2 to 6carbon atoms wherein some or all of the hydrogen atoms may be replacedby straight or branched alkyl or alkoxy groups of 1 to 4 carbon atoms,nitro, acetyl, or phenyl groups. R¹ll is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, alkenyl, alkoxyalkyl, phenyl ornaphthyl group wherein some or all of the hydrogen atoms may be replacedby alkyl or alkoxy groups of 1 to 4 carbon atoms, phenyl groups (whichmay have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms,nitro, or acetyl group), hetero-aromatic groups of 3 to 5 carbon atoms,or chlorine or fluorine atoms.

[0101] Of the groups represented by R¹¹⁰, exemplary arylene groupsinclude 1,2-phenylene and 1,8-naphthylene; exemplary alkylene groupsinclude methylene, 1,2-ethylene, 1,3-propylene, 1,4-butylene,1-phenyl-1,2-ethylene, and norbornane-2,3-diyl; and exemplary alkenylenegroups include 1,2-vinylene, 1-phenyl-1,2-vinylene, and5-norbornene-2,3-diyl. Of the groups represented by R¹¹¹, exemplaryalkyl groups are as exemplified for R^(101a) to R^(101c); exemplaryalkenyl groups include vinyl, 1-propenyl, allyl, 1-butenyl, 3-butenyl,isoprenyl, 1-pentenyl, 3-pentenyl, 4-pentenyl, dimethylallyl, 1-hexenyl,3-hexenyl, 5-hexenyl, 1-heptenyl, 3-heptenyl, 6-heptenyl, and 7-octenyl;and exemplary alkoxyalkyl groups include methoxymethyl, ethoxymethyl,propoxymethyl, butoxymethyl, pentyloxymethyl, hexyloxymethyl,heptyloxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl,pentyloxyethyl, hexyloxyethyl, methoxypropyl, ethoxypropyl,propoxypropyl, butoxypropyl, methoxybutyl, ethoxybutyl, propoxybutyl,methoxypentyl, ethoxypentyl, methoxyhexyl, and methoxyheptyl.

[0102] Of the substituents on these groups, the alkyl groups of 1 to 4carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyland tert-butyl; the alkoxy groups of 1 to 4 carbon atoms includemethoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, andtert-butoxy; the phenyl groups which may have substituted thereon analkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group includephenyl, tolyl, p-tert-butoxyphenyl, p-acetylphenyl and p-nitrophenyl;the hetero-aromatic groups of 3 to 5 carbon atoms include pyridyl andfuryl.

[0103] Illustrative examples of the photoacid generator include:

[0104] onium salts such as diphenyliodonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate,diphenyliodonium p-toluene-sulfonate,(p-tert-butoxyphenyl)phenyliodonium p-toluene-sulfonate,triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,triphenylsulfonium nonafluorobutane-sulfonate, triphenylsulfoniumbutanesulfonate, trimethylsulfonium trifluoromethanesulfonate,trimethylsulfonium p-toluenesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl) sulfonium p-toluenesulfonate,dimethylphenylsulfonium trifluoromethanesulfonate,dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfoniumtrifluoromethanesulfonate, dicyclohexylphenylsulfoniump-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocyclohexyl) sulfoniumtrifluoromethanesulfonate,ethylenebis-[methyl(2-oxocyclopentyl)sulfoniumtrifluoromethanesulfonate], and1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;

[0105] diazomethane derivatives such asbis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane,bis(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl) diazomethane,bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane,bis(n-propylsulfonyl) diazomethane, bis(isopropylsulfonyl)diazomethane,bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl) diazomethane,bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane,bis(tert-amylsulfonyl) diazomethane,1-cyclohexylsulfonyl-1-(tert-butylsulfonyl) diazomethane,1-cyclohexylsulfonyl-1-(tert-amylsulfonyl) diazomethane, and1-tert-amylsulfonyl-1-(tert-butylsulfonyl) diazomethane;

[0106] glyoxime derivatives such asbis-o-(p-toluenesulfonyl)-α-dimethylglyoxime,bis-o-(p-toluenesulfonyl)-α-diphenylglyoxime, bis-o-(p-toluenesulfonyl)-α-dicyclohexylglyoxime, glyoxime,bis-o-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-o-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(n-butanesulfonyl)-α-dimethylglyoxime,bis-o-(n-butanesulfonyl)-α-diphenylglyoxime,bis-o-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-o-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,bis-o-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(methanesulfonyl)-α-dimethylglyoxime,bis-o-(trifluoromethanesulfonyl)-α-dimethylglyoxime,bis-o-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-o-(tert-butanesulfonyl)-α-dimethylglyoxime,bis-o-(perfluorooctanesulfonyl)-α-dimethylglyoxime,bis-o-(cyclohexanesulfonyl)-α-dimethylglyoxime,bis-o-(benzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-o-(xylenesulfonyl)-α-dimethylglyoxime, andbis-o-(camphorsulfonyl)-α-dimethylglyoxime;

[0107] bissulfone derivatives such as bisnaphthylsulfonylmethane,bistrifluoromethylsulfonylmethane, bismethylsulfonylmethane,bisethylsulfonylmethane, bispropylsulfonylmethane,bisisopropylsulfonylmethane, bis-p-toluenesulfonylmethane, andbisbenzenesulfonylmethane;

[0108] β-ketosulfone derivatives such as2-cyclohexylcarbonyl-2-(p-toluenesulfonyl) propane and2-isopropyl-carbonyl-2-(p-toluenesulfonyl) propane;

[0109] disulfone derivatives such as diphenyl disulfone and dicyclohexyldisulfone;

[0110] nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzylp-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;

[0111] sulfonic acid ester derivatives such as1,2,3-tris-(methanesulfonyloxy) benzene,1,2,3-tris(trifluoromethanesulfonyloxy) benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; and

[0112] sulfonic acid esters of N-hydroxyimides such asN-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimidetrifluoromethanesulfonate, N-hydroxysuccinimide ethanesulfonate,N-hydroxysuccinimide 1-propanesulfonate, N-hydroxysuccinimide2-propanesulfonate, N-hydroxysuccinimide 1-pentanesulfonate,N-hydroxysuccinimide 1-octanesulfonate, N-hydroxysuccinimidep-toluenesulfonate, N-hydroxysuccinimide p-methoxybenzenesulfonate,N-hydroxysuccinimide 2-chloroethanesulfonate, N-hydroxysuccinimidebenzenesulfonate, N-hydroxysuccinimide 2,4,6-trimethylbenzenesulfonate,N-hydroxysuccinimide 1-naphthalenesulfonate, N-hydroxysuccinimide2-naphthalenesulfonate, N-hydroxy-2-phenylsuccinimide methanesulfonate,N-hydroxymaleimide methanesulfonate, N-hydroxymaleimide ethanesulfonate,N-hydroxy-2-phenylmaleimide methanesulfonate, N-hydroxyglutarimidemethanesulfonate, N-hydroxyglutarimide benzenesulfonate,N-hydroxyphthalimide methanesulfonate, N-hydroxyphthalimidebenzenesulfonate, N-hydroxyphthalimide trifluoromethanesulfonate,N-hydroxyphthalimide p-toluenesulfonate, N-hydroxynaphthalimidemethanesulfonate, N-hydroxynaphthalimide benzenesulfonate,N-hydroxy-5-norbornene-2,3-dicarboxyimide methanesulfonate,N-hydroxy-5-norbornene-2,3-dicarboxyimide trifluoromethanesulfonate, andN-hydroxy-5-norbornene-2,3-dicarboxyimide p-toluenesulfonate.

[0113] Preferred among these photoacid generators are onium salts suchas triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfoniump-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoromethanesulfonate,and 1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane,bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane,bis(isopropylsulfonyl)diazomethane, and bis(tert-butylsulfonyl)diazomethane; glyoxime derivatives such asbis-o-(p-toluenesulfonyl)-α-dimethylglyoxime andbis-o-(n-butanesulfonyl)-α-dimethylglyoxime; bissulfone derivatives suchas bisnaphthylsulfonylmethane; and sulfonic acid esters ofN-hydroxyimide compounds such as N-hydroxysuccinimide methanesulfonate,N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate,N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimidep-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, andN-hydroxynaphthalimide benzenesulfonate.

[0114] These photoacid generators may be used singly or in combinationsof two or more thereof. Onium salts are effective for improvingrectangularity, while diazomethane derivatives and glyoxime derivativesare effective for reducing standing waves. The combination of an oniumsalt with a diazomethane or a glyoxime derivative allows for fineadjustment of the profile.

[0115] The photoacid generator is added in an amount of 0.1 to 15 parts,and especially 0.5 to 8 parts by weight, per 100 parts by weight of thebase resin (all parts are by weight, hereinafter). Less than 0.1 part ofthe photoacid generator would provide a poor sensitivity whereas morethan 15 parts of the photoacid generator would adversely affecttransparency and resolution.

[0116] Organic Solvent

[0117] The organic solvent used herein may be any organic solvent inwhich the base resin, photoacid generator, and other components aresoluble. Illustrative, non-limiting, examples of the organic solventinclude ketones such as cyclohexanone and methyl-2-n-amylketone;alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol,1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propyleneglycol monomethyl ether, ethylene glycol monomethyl ether, propyleneglycol monoethyl ether, ethylene glycol monoethyl ether, propyleneglycol dimethyl ether, and diethylene glycol dimethyl ether; and esterssuch as propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butylacetate, tert-butyl propionate, and propylene glycol mono-tert-butylether acetate. These solvents may be used alone or in combinations oftwo or more thereof. Of the above organic solvents, it is recommended touse diethylene glycol dimethyl ether and 1-ethoxy-2-propanol because thephotoacid generator serving as one of the resist components is mostsoluble therein, propylene glycol monomethyl ether acetate because it isa safe solvent, or a mixture thereof.

[0118] An appropriate amount of the organic solvent used is about 200 to1,000 parts, especially about 400 to 800 parts by weight per 100 partsby weight of the base resin.

[0119] Other Polymer

[0120] To the resist composition of the invention, another polymer otherthan the inventive polymer comprising recurring units of formula (1a-1)and/or (1a-2) may also be added. The other polymers that can be added tothe resist composition are, for example, those polymers comprising unitsof the following formula (R1) or (R2) and having a weight averagemolecular weight of about 1,000 to about 500,000, especially about 5,000to about 100,000 although the other polymers are not limited thereto.

[0121] Herein, R⁰⁰¹ is hydrogen, methyl or CH₂CO₂R⁰⁰³. R⁰⁰² is hydrogen,methyl or CO₂R⁰⁰³. R⁰⁰³ is a straight, branched or cyclic alkyl group of1 to 15 carbon atoms. R⁰⁰⁴ is hydrogen or a monovalent hydrocarbon groupof 1 to 15 carbon atoms having a carboxyl or hydroxyl group. At leastone of R⁰⁰⁵ to R⁰⁰⁸ represents a monovalent hydrocarbon group of 1 to 15carbon atoms having a carboxyl or hydroxyl group while the remaining R'sindependently represent hydrogen or a straight, branched or cyclic alkylgroup of 1 to 15 carbon atoms. Alternatively, R⁰⁰⁵ to R⁰⁰⁸, takentogether, may form a ring, and in that event, at least one of R⁰⁰⁵ toR⁰⁰⁸ is a divalent hydrocarbon group of 1 to 15 carbon atoms having acarboxyl or hydroxyl group, while the remaining R's are independentlysingle bonds or straight, branched or cyclic alkylene groups of 1 to 15carbon atoms. R⁰⁰⁹ is a monovalent hydrocarbon group of 3 to 15 carbonatoms containing a —CO₂— partial structure. At least one of Rolo to R⁰¹³is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing a—CO₂— partial structure, while the remaining R's are independentlyhydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbonatoms. R⁰¹⁰ to R⁰¹³, taken together, may form a ring, and in that event,at least one of R⁰¹⁰ to R⁰¹³ is a divalent hydrocarbon group of 1 to 15carbon atoms containing a —CO₂— partial structure, while the remainingR's are independently single bonds or straight, branched or cyclicalkylene groups of 1 to 15 carbon atoms. R⁰¹⁴ is a polycyclichydrocarbon group having 7 to 15 carbon atoms or an alkyl groupcontaining a polycyclic hydrocarbon group. R⁰¹⁵ is an acid labile group.R⁰¹⁶ is hydrogen or methyl. R⁰¹⁷ is a straight, branched or cyclic alkylgroup of 1 to 8 carbon atoms. Letter k′ is equal to 0 or 1; a1′, a2′,a3′, b1′, b2′, b3′, c1′, c2′, c3′, d1′, d2′, d3′, and e′ are numbersfrom 0 to less than 1, satisfyinga1′+a2′+a3′+b1′+b2′+b3′+c1′+c2′+c3′+d1′+d2′+d3′+e′=1; f′, g′, h′, i′,and j′ are numbers from 0 to less than 1, satisfying f′+g′+h′+i′+j′=1.X′, y′ and z′ are integers of 0 to 3, satisfying x′+y′+z′<5 and 1≦y′+Z′.

[0122] Exemplary groups of these R's are as exemplified above for R¹ toR¹⁵.

[0123] The inventive polymer (comprising recurring units of formula(1a-1) and/or (1a-2)) and the other polymer are preferably blended in aweight ratio from 10:90 to 90:10, more preferably from 20:80 to 80:20.If the blend ratio of the inventive polymer is below this range, theresist composition would become poor in some of the desired properties.The properties of the resist composition can be adjusted by properlychanging the blend ratio of the inventive polymer.

[0124] The other polymer is not limited to one type and a mixture of twoor more other polymers may be added. The use of plural polymers allowsfor easy adjustment of resist properties.

[0125] Dissolution Regulator

[0126] To the resist composition, a dissolution regulator may be added.The dissolution regulator is a compound having on the molecule at leasttwo phenolic hydroxyl groups, in which an average of from 0 to 100 mol %of all the hydrogen atoms on the phenolic hydroxyl groups are replacedwith acid labile groups or a compound having on the molecule at leastone carboxyl group, in which an average of 50 to 100 mol % of all thehydrogen atoms on the carboxyl groups are replaced with acid labilegroups, both the compounds having an average molecular weight within arange of 100 to 1,000, and preferably 150 to 800.

[0127] The degree of substitution of the hydrogen atoms on the phenolichydroxyl groups with acid labile groups is on average at least 0 mol %,and preferably at least 30 mol %, of all the phenolic hydroxyl groups.The upper limit is 100 mol %, and preferably 80 mol %. The degree ofsubstitution of the hydrogen atoms on the carboxyl groups with acidlabile groups is on average at least 50 mol %, and preferably at least70 mol %, of all the carboxyl groups, with the upper limit being 100 mol%.

[0128] Preferable examples of such compounds having two or more phenolichydroxyl groups or compounds having at least one carboxyl group includethose of formulas (D1) to (D14) below.

[0129] In these formulas, R²⁰¹ and R²⁰² are each hydrogen or a straightor branched alkyl or alkenyl of 1 to 8 carbon atoms; R²⁰³ is hydrogen, astraight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or-(R²⁰⁷)_(h)-COOH; R²⁰⁴ is —(CH₂)_(i)— (where i=2 to 10), an arylene of 6to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfuratom; R²⁰⁵ is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R²⁰⁶is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbonatoms, or a hydroxyl-substituted phenyl or naphthyl; R²⁰⁷ is a straightor branched alkylene of 1 to 10 carbon atoms; R²⁰⁸ is hydrogen orhydroxyl; the letter j is an integer from 0 to 5; u and h are each 0 or1; s, t, s′, t′, s″, and t″ are each numbers which satisfy s+t =8,s′+t′=5, and s″+t″=4, and are such that each phenyl skeleton has atleast one hydroxyl group; and a is a number such that the compounds offormula (D8) or (D9) have a molecular weight of from 100 to 1,000.

[0130] In the above formulas, suitable examples of R²⁰¹ and R²⁰² includehydrogen, methyl, ethyl, butyl, propyl, ethynyl, and cyclohexyl;suitable examples of R²⁰³ include the same groups as for R²⁰¹ and R²⁰²,as well as —COOH and —CH₂COOH; suitable examples of R²⁰⁴ includeethylene, phenylene, carbonyl, sulfonyl, oxygen, and sulfur; suitableexamples of R²⁰⁵ include methylene as well as the same groups as forR²⁰⁴; and suitable examples of R²⁰⁶ include hydrogen, methyl, ethyl,butyl, propyl, ethynyl, cyclohexyl, and hydroxyl-substituted phenyl ornaphthyl.

[0131] Exemplary acid labile groups on the dissolution regulator includegroups of the following general formulae (L1) to (L4), tertiary alkylgroups of 4 to 20 carbon atoms, trialkylsilyl groups in which each ofthe alkyls has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20carbon atoms.

[0132] In these formulas, R^(L01) and R^(L02) are each hydrogen or astraight, branched or cyclic alkyl having 1 to 18 carbon atoms; andR^(L03) is a monovalent hydrocarbon group of 1 to 18 carbon atoms whichmay contain a heteroatom (e.g., oxygen). A pair of R^(L01) and R^(L02),a pair of R^(L01) and R^(L03) or a pair of R^(L02) and R^(L03) maytogether form a ring, with the proviso that R^(L01), R^(L02), andR^(L03) are each a straight or branched alkylene of 1 to 18 carbon atomswhen they form a ring. R^(L04) is a tertiary alkyl group of 4 to 20carbon atoms, a trialkysilyl group in which each of the alkyls has 1 to6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group ofthe formula (L1). R^(L05) is a straight, branched or cyclic alkyl groupof 1 to 8 carbon atoms or a substituted or unsubstituted aryl group of 6to 20 carbon atoms. R^(L06) is a straight, branched or cyclic alkylgroup of 1 to 8 carbon atoms or a substituted or unsubstituted arylgroup of 6 to 20 carbon atoms. R^(L07) to R^(L16) independentlyrepresent hydrogen or monovalent hydrocarbon groups of 1 to 15 carbonatoms which may contain a hetero atom. Alternatively, R^(L07) toR^(L16), taken together, may form a ring. Each of R^(L07) to R^(L16)represents a divalent C₁-C₁₅ hydrocarbon group which may contain ahetero atom, when they form a ring. Two of R^(L07) to R^(L16) which areattached to adjoining carbon atoms may bond together directly to form adouble bond. Letter y is an integer of 0 to 6. Letter m is equal to 0 or1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or 3.

[0133] The dissolution regulator may be formulated in an amount of 0 to50 parts, preferably 5 to 50 parts, and more preferably 10 to 30 parts,per 100 parts of the base resin, and may be used singly or as a mixtureof two or more thereof. Less than 5 parts of the dissolution regulatormay fail to yield an improved resolution, whereas the use of more than50 parts would lead to slimming of the patterned film, and thus adecline in resolution.

[0134] The dissolution regulator can be synthesized by introducing acidlabile groups into a compound having phenolic hydroxyl or carboxylgroups in accordance with an organic chemical formulation.

[0135] Basic Compound

[0136] In the resist composition of the invention, a basic compound maybe blended. A suitable basic compound used herein is a compound capableof suppressing the rate of diffusion when the acid generated by thephotoacid generator diffuses within the resist film. The inclusion ofthis type of basic compound holds down the rate of acid diffusion withinthe resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure, thus reducingsubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile.

[0137] Examples of basic compounds include primary, secondary, andtertiary aliphatic amines, mixed amines, aromatic amines, heterocyclicamines, carboxyl group-bearing nitrogenous compounds, sulfonylgroup-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenouscompounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholicnitrogenous compounds, amide derivatives, and imide derivatives.

[0138] Examples of suitable primary aliphatic amines include ammonia,methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, di-n-propylamine,di-iso-propylamine, di-n-butylamine, di-iso-butylamine,di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didodecylamine, dicetylamine,N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyltetraethylenepentamine.

[0139] Examples of suitable mixed amines include dimethylethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine. Examples of suitable aromatic and heterocyclicamines include aniline derivatives (e.g., aniline, N-methylaniline,N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline,3-methylaniline, 4-methylaniline, ethylaniline, propylaniline,trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline,2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, andN,N-dimethyltoluidine), diphenyl(p-tolyl) amine, methyldiphenylamine,triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene,pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazolederivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g.,thiazole and isothiazole), imidazole derivatives (e.g., imidazole,4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazolederivatives, furazan derivatives, pyrroline derivatives (e.g., pyrrolineand 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),imidazoline derivatives, imidazolidine derivatives, pyridine derivatives(e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine,butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine,trimethylpyridine, triethylpyridine, phenylpyridine,3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine,benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine,1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1H-indazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

[0140] Examples of suitable carboxyl group-bearing nitrogenous compoundsinclude aminobenzoic acid, indolecarboxylic acid, and amino acidderivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid,glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples ofsuitable sulfonyl group-bearing nitrogenous compounds include3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples ofsuitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenylgroup-bearing nitrogenous compounds, and alcoholic nitrogenous compoundsinclude 2-hydroxypyridine, aminocresol, 2,4-quinolinediol,3-indolemethanol hydrate, monoethanolamine, diethanolamine,triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine,triisopropanolamine, 2,21-iminodiethanol, 2-aminoethanol,3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl) morpholine,2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl) piperazine,1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol,1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidineethanol, 1-aziridine ethanol, N-(2-hydroxyethyl) phthalimide, andN-(2-hydroxyethyl)isonicotinamide. Examples of suitable amidederivatives include formamide, N-methylformamide, N,N-dimethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, andbenzamide. Suitable imide derivatives include phthalimide, succinimide,and maleimide.

[0141] In addition, basic compounds of the following general formula(Bl) may also be included alone or in admixture.

N(X)_(n)(Y)_(3−n)  B1

[0142] In the formula, n is equal to 1, 2 or 3; Y is independentlyhydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbonatoms which may contain a hydroxyl group or ether; and X isindependently selected from groups of the following general formulas(Xl) to (X3), and two or three X's may bond together to form a ring.

[0143] In the formulas, R³⁰⁰, R³⁰² and R³⁰⁵ are independently straightor branched alkylene groups of 1 to 4 carbon atoms; R³⁰¹ and R³⁰⁴ areindependently hydrogen, straight, branched or cyclic alkyl groups of 1to 20 carbon atoms, which may contain at least one hydroxyl group,ether, ester or lactone ring; and R³⁰³ is a single bond or a straight orbranched alkylene group of 1 to 4 carbon atoms.

[0144] Illustrative examples of the compounds of formula (B1) includetris(2-methoxymethoxyethyl)amine, tris{2-(methoxyethoxy) ethyl}amine,tris{2-(2-methoxyethoxy-methoxy) ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxy-propoxy) ethyl)amine,tris[2-{2-(2-hydroxyethoxy)ethoxy}-ethyl]amine,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane,4,7,13,18-tetraoxa-1,10-diazabicyclo-[8.5.5]eicosane,1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane,1-aza-12-crown-4,1-aza-15-crown-5, 1-aza-18-crown-6,tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine,tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl) amine,tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)amine,tris(2-pivaloyloxyethyl)amine,N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine,tris(2-methoxycarbonyloxyethyl)amine,tris(2-tert-butoxycarbonyloxyethyl) amine,tris[2-(2-oxopropoxy)ethyl]amine,tris[2-(methoxycarbonylmethyl)oxyethyl]amine,tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine,tris[2-(cyclohexyloxycarbonylmethyloxy) ethyl]amine,tris(2-methoxycarbonylethyl) amine, tris(2-ethoxycarbonylethyl)amine,N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl) ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl) ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl) ethylamine,N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl) methoxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl) methoxycarbonyl]ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl) ethylamine,N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]-ethylamine,N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl) ethylamine,N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl) ethylamine,N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl) ethylamine,N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl) ethylamine,N-(2-hydroxyethyl)-bis [2-(methoxycarbonyl)ethyllamine,N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyllamine,N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(2-methoxyethoxycarbonyl) ethyl]amine,N-methyl-bis(2-acetoxyethyl) amine, N-ethyl-bis(2-acetoxyethyl)amine,N-methyl-bis (2-pivaloyloxyethyl)amine,N-ethyl-bis[2-(methoxycarbonyloxy) ethyl]amine,N-ethyl-bis[2-(tert-butoxycarbonyloxy) ethyl]amine,tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine,N-butyl-bis (methoxycarbonylmethyl)amine,N-hexyl-bis(methoxycarbonylmethyl) amine, andP-(diethylamino)-8-valerolactone.

[0145] The basic compound is preferably formulated in an amount of 0.001to 10 parts, and especially 0.01 to 1 part, per part of the photoacidgenerator. Less than 0.001 part of the basic compound fails to achievethe desired effects thereof, while the use of more than 10 parts wouldresult in too low a sensitivity and resolution.

[0146] Other Components

[0147] In the resist composition, a compound bearing a ≡C—COOH group ina molecule may be blended. Exemplary, non-limiting compounds bearing a≡C—COOH group include one or more compounds selected from Groups I andII below. Including this compound improves the PED stability of theresist and ameliorates edge roughness on nitride film substrates.

[0148] Group I:

[0149] Compounds in which some or all of the hydrogen atoms on thephenolic hydroxyl groups of the compounds of general formulas (A1) to(A10) below have been replaced with -R⁴⁰¹-COOH (wherein R⁴⁰¹ is astraight or branched alkylene of 1 to 10 carbon atoms), and in which themolar ratio C/(C+D) of phenolic hydroxyl groups (C) to ≡C—COOH groups(D) in the molecule is from 0.1 to 1.0.

[0150] In these formulas, R⁴⁰⁸ is hydrogen or methyl; R⁴⁰² and R⁴⁰³ areeach hydrogen or a straight or branched alkyl or alkenyl of 1 to 8carbon atoms; R⁴⁰⁴ is hydrogen, a straight or branched alkyl or alkenylof 1 to 8 carbon atoms, or a -(R⁴⁰⁹)_(h)-COOR′ group (R′ being hydrogenor -R⁴⁰⁹-COOH); R⁴⁰⁵ is —(CH₂)— (wherein i is 2 to 10), an arylene of 6to 10 carbon 10 atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfuratom; R⁴⁰⁶ is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R⁴⁰⁷is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbonatoms, or a hydroxyl-substituted phenyl or naphthyl; R⁴⁰⁹ is a straightor branched alkylene of 1 to 10 carbon atoms; R⁴¹⁰ is hydrogen, astraight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a-R⁴¹¹-COOH group; R⁴¹¹ is a straight or branched alkylene of 1 to 10carbon atoms; the letter j is an integer from 0 to 5; u and h are each 0or 1; s1, t1, s2, t2, s3, t3, s4, and t4 are each numbers which satisfys1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6, and are such that each phenylskeleton has at least one hydroxyl group; κ is a number such that thecompound of formula (A6) may have a weight average molecular weight of1,000 to 5,000; and λ is a number such that the compound of formula (A7)may have a weight average molecular weight of 1,000 to 10,000.

[0151] Group II:

[0152] Compounds of general formulas (A11) to (A15) below.

[0153] In these formulas, R⁴⁰², R⁴⁰³, and R⁴¹¹ are as defined above;R⁴¹² is hydrogen or hydroxyl; s5 and t5 are numbers which satisfy s5≧0,t5≧0, and s5+t5=5; and h′ is equal to 0 or 1.

[0154] Illustrative, non-limiting examples of the compound bearing a≡C—COOH group include compounds of the general formulas AI-1 to AI-14and AII-1 to AII-10 below.

[0155] In the above formulas, R″ is hydrogen or a CH₂COOH group suchthat the CH₂COOH group accounts for 10 to 100 mol % of R″ in eachcompound, α and κ are as defined above.

[0156] The compound bearing a ≡C—COOH group within the molecule may beused singly or as combinations of two or more thereof.

[0157] The compound bearing a ≡C—COOH group within the molecule is addedin an amount ranging from 0 to 5 parts, preferably 0.1 to 5 parts, morepreferably 0.1 to 3 parts, further preferably 0.1 to 2 parts, per 100parts of the base resin. More than 5 parts of the compound can reducethe resolution of the resist composition.

[0158] The resist composition of the invention may additionally includean acetylene alcohol derivative for the purpose of enhancing the shelfstability. Preferred acetylene alcohol derivatives are those having thegeneral formula (S1) or (S2) below.

[0159] In the formulas, R⁵⁰¹, R⁵⁰², R⁵⁰³, R⁵⁰⁴, and R⁵⁰⁵ are eachhydrogen or a straight, branched, or cyclic alkyl of 1 to 8 carbonatoms; and X and Y are each 0 or a positive number, satisfying 0≦X≦30,0≦Y≦30, and 0≦X+Y≦40.

[0160] Preferable examples of the acetylene alcohol derivative includeSurfynol 61, Surfynol 82, Surfynol 104, Surfynol 104E, Surfynol 104H,Surfynol 104A, Surfynol TG, Surfynol PC, Surfynol 440, Surfynol 465, andSurfynol 485 from Air Products and Chemicals Inc., and Surfynol E1004from Nisshin Chemical Industry K.K.

[0161] The acetylene alcohol derivative is preferably added in an amountof 0.01 to 2% by weight, and more preferably 0.02 to 1% by weight, per100% by weight of the resist composition. Less than 0.01% by weightwould be ineffective for improving coating characteristics and shelfstability, whereas more than 2% by weight would result in a resisthaving a low resolution.

[0162] The resist composition of the invention may include, as anoptional ingredient, a surfactant which is commonly used for improvingthe coating characteristics. Optional ingredients may be added inconventional amounts so long as this does not compromise the objects ofthe invention.

[0163] Nonionic surfactants are preferred, examples of which includeperfluoroalkylpolyoxyethylene ethanols, fluorinated alkyl esters,perfluoroalkylamine oxides, perfluoroalkyl EO-addition products, andfluorinated organosiloxane compounds. Useful surfactants arecommercially available under the trade names Florade FC-430 and FC-431from Sumitomo 3M K.K., Surflon S-141 and S-145 from Asahi Glass K.K.,Unidine DS-401, DS-403 and DS-451 from Daikin Industry K.K., MegafaceF-8151 from Dai-Nippon Ink & Chemicals K.K., and X-70-092 and X-70-093from Shin-Etsu Chemical Co., Ltd. Preferred surfactants are FloradeFC-430 from Sumitomo 3M K.K. and X-70-093 from Shin-Etsu Chemical Co.,Ltd.

[0164] Pattern formation using the resist composition of the inventionmay be carried out by a known lithographic technique. For example, theresist composition is applied onto a substrate such as a silicon waferby spin coating or the like to form a resist film having a thickness of0.3 to 2.0 μm, which is then pre-baked on a hot plate at 60 to 150° C.for 1 to 10 minutes, and preferably at 80 to 130° C. for 1 to 5 minutes.A patterning mask having the desired pattern is then placed over theresist film, and the film exposed through the mask to an electron beamor to high-energy radiation such as deep-UV rays, an excimer laser, orx-rays in a dose of about 1 to 200 mJ/cm², and preferably about 10 to100 mJ/cm², then post-exposure baked (PEB) on a hot plate at 60 to 150°C. for 1 to 5 minutes, and preferably at 80 to 130° C. for 1 to 3minutes. Finally, development is carried out using as the developer anaqueous alkali solution, such as a 0.1 to 5% (preferably 2 to 3%)aqueous solution of tetramethylammonium hydroxide (TMAH), this beingdone by a conventional method such as dipping, puddling, or spraying fora period of 0.1 to 3 minutes, and preferably 0.5 to 2 minutes. Thesesteps result in the formation of the desired pattern on the substrate.Of the various types of high-energy radiation that may be used, theresist composition of the invention is best suited to fine patternformation with, in particular, deep-UV rays having a wavelength of 248to 193 nm, an excimer laser, x-rays, or an electron beam. The desiredpattern may not be obtainable outside the upper and lower limits of theabove range.

[0165] The resist composition comprising the polymer as a base resinlends itself to micropatterning with electron beams or deep-UV rayssince it is sensitive to high-energy radiation and has excellentsensitivity, resolution, and etching resistance. Especially because ofthe minimized absorption at the exposure wavelength of an ArF or KrFexcimer laser, a finely defined pattern having sidewalls perpendicularto the substrate can easily be formed.

EXAMPLE

[0166] Synthesis Examples and Examples are given below by way ofillustration and not by way of limitation.

Synthesis Examples

[0167] Ester compounds and polymers containing the same were synthesizedaccording to the following formulation.

Synthesis Example 1-1 Synthesis of Monomer 1

[0168] In 500 ml of diethyl ether was dissolved 168.0 g ofchlorocyclohexane. Below 60° C., this reaction mixture was addeddropwise to 26.4 g of metallic magnesium over one hour. After agitationwas continued for 2 hours at room temperature, 84.0 g of cyclopentanonewas added dropwise over 45 minutes to the reaction mixture which waskept below 65° C. After agitation was continued for one hour at roomtemperature, the reaction solution was worked up in a conventionalmanner. The resulting oily substance was distilled in vacuum, collecting97.3 g of 1-cyclohexylcyclopentanol. The yield was 57.9%.

[0169] In 1 liter of methylene chloride was dissolved 92.4 g of1-cyclohexylcyclopentanol. To the solution below −20° C, 74.3 g ofacrylic chloride was added dropwise over 10 minutes. To the reactionmixture, 1.0 g of 4-(N,N-dimethylamino) pyridine was added and then,125.0 g of triethylamine was added dropwise over one hour and below −20°C. This reaction mixture was agitated for 15 hours at room temperatureand subjected to conventional post-treatment, obtaining about 130 g ofan oily substance. This was used in the subsequent reaction withoutpurification.

[0170] The oily substance obtained in the above step was dissolved in300 ml of benzene. To this solution below 10° C., 72.6 g ofcyclopentadiene was added dropwise over 10 minutes. The reaction mixturewas agitated for 17 hours at room temperature, then for one hour at 70°C., and concentrated in vacuum. Vacuum distillation (170° C./0.2 Torr)of the resulting oily substance yielded 106.6 g of1-cyclohexylcyclopentyl 5-norbornene-2-carboxylate (designated Monomer1). The yield was 67.3%.

[0171]FIG. 1 shows the spectrum of Monomer 1 by ¹H-NMR (CDCl₃, 270 MHz).

Synthesis Examples 1-2 to 1-8 Synthesis of Monomers 2 to 8

[0172] Monomers 2 to 8 were synthesized by the same procedure as aboveor a well-known procedure.

Synthesis Example 2-1 Synthesis of Polymer 1

[0173] In 1 liter of tetrahydrofuran, 72.0 g of Monomer 1 and 24.5 g ofmaleic anhydride were dissolved, and 1.8 g of2,2′-azobisisobutyronitrile added. After agitation was continued for 15hours at 60° C., the reaction solution was concentrated in vacuum. Theresidue was dissolved in 400 ml of tetrahydrofuran, which was, in turn,added dropwise to 10 liters of n-hexane. The resulting solids werecollected by filtration, washed with 10 liters of n-hexane, and dried invacuum at 40° C. for 6 hours, obtaining 53.6 g of a polymer, designatedPolymer 1. The yield was 55.5%.

Synthesis Examples 2-2 to 2-18 Synthesis of Polymers 2 to 18

[0174] Polymers 2 to 18 were synthesized by the same procedure as aboveor a well-known procedure.

Example I

[0175] Resist compositions were formulated using inventive polymers andexamined for resolution upon KrF excimer laser exposure.

Examples I-1 to I-28 Evaluation of Resist Resolution

[0176] Resist compositions were prepared by using Polymers 1 to 18 asthe base resin, and dissolving the polymer, a photoacid generator(designated as PAG 1 and 2), a dissolution regulator (designated as DRR1 to 4), a basic compound, and a compound having a ≡C—COOH group in themolecule (ACC 1 and 2) in a solvent in accordance with the formulationshown in Tables 1 and 2. These compositions were each filtered through aTeflon filter (pore diameter 0.2 μm), thereby giving resist solutions.

[0177] The solvents and basic compounds used are as follows. It is notedthat the solvents contained 0.01% by weight of surfactant Florade FC-430(Sumitomo 3M).

[0178] PGMEA: propylene glycol methyl ether acetate CyHO: cyclohexanoneTBA: tributylamine TEA: triethanolamine TMMEA:trismethoxymethoxyethylamine TMEMEA: trismethoxyethoxymethoxyethylamine

[0179] These resist solutions were spin-coated onto silicon wafers, thenbaked on a hot plate at 110° C. for 90 seconds to give resist filmshaving a thickness of 0.5 μm. The resist films were exposed using an KrFexcimer laser stepper (Nikon Corporation; NA 0.5), then baked (PEB) at110° C. for 90 seconds, and developed with a solution of 2.38% TMAH inwater, thereby giving positive patterns.

[0180] The resulting resist patterns were evaluated as described below.First, the sensitivity (Eth, mJ/cm²) was determined. Next, the optimaldose (Eop, mJ/cm²) was defined as the dose which provides a 1:1resolution at the top and bottom of a 0.30 μm line-and-space pattern,and the resolution of the resist under evaluation was defined as theminimum line width (pm) of the lines and spaces that separated at thisdose. The shape of the resolved resist pattern was examined under ascanning electron microscope.

[0181] The composition and test results of the resist materials areshown in Tables 1 and 2.

Comparative Example

[0182] For comparison purposes, resist compositions were formulated andexamined for resolution upon KrF excimer laser exposure.

Comparative Examples 1 to 4

[0183] Resist compositions were prepared as in Example I except thatPolymers 19 and 20 shown below were used as the base resin, inaccordance with the formulation shown in Table 3.

[0184] These resist materials were similarly evaluated. The compositionand test results of these resist materials are shown in Table 3. TABLE 1Photoacid Dissolution Basic Optimum Base resin generator regulatorcompound Solvent dose Resolution Example (pbw) (pbw) (pbw) (pbw) (pbw)(mJ/cm²) (μm) Shape I-1 Polymer 1 PAG 1 TBA PGMEA 24.0 0.22 rectangular(80) (1) (0.078) (480) I-2 Polymer 2 PAG 1 TBA PGMEA 20.0 0.22rectangular (80) (1) (0.078) (480) I-3 Polymer 3 PAG 1 TBA PGMEA 23.00.22 rectangular (80) (1) (0.078) (480) I-4 Polymer 4 PAG 1 TBA PGMEA21.5 0.22 rectangular (80) (1) (0.078) (480) I-5 Polymer 5 PAG 1 TBAPGMEA 24.5 0.22 rectangular (80) (1) (0.078) (480) I-6 Polymer 6 PAG 1TBA PGMEA 19.5 0.22 rectangular (80) (1) (0.078) (480) I-7 Polymer 7 PAG1 TBA PGMEA 25.0 0.22 rectangular (80) (1) (0.078) (480) I-8 Polymer 8PAG 1 TBA PGMEA 22.5 0.22 rectangular (80) (1) (0.078) (480) I-9 Polymer9 PAG 1 TBA PGMEA 22.0 0.22 rectangular (80) (1) (0.078) (480) I-10Polymer 10 PAG 1 TBA PGMEA 25.5 0.22 rectangular (80) (1) (0.078) (480)I-11 Polymer 11 PAG 1 TBA PGMEA 22.5 0.22 rectangular (80) (1) (0.078)(480) I-12 Polymer 12 PAG 1 TBA PGMEA 22.5 0.22 rectangular (80) (1)(0.078) (480) I-13 Polymer 13 PAG 1 TBA CyHO 18.0 0.22 rectangular (80)(1) (0.078) (640) I-14 Polymer 14 PAG 1 TBA CyHO 16.5 0.22 rectangular(80) (1) (0.078) (640) I-15 Polymer 15 PAG 1 TBA CyHO 16.0 0.22rectangular (80) (1) (0.078) (640) I-16 Polymer 16 PAG 1 TBA CyHO 21.50.22 rectangular (80) (1) (0.078) (640) I-17 Polymer 17 PAG 1 TBA CyHO20.5 0.22 rectangular (80) (1) (0.078) (640) I-18 Polymer 18 PAG 1 TBACyHO 20.0 0.22 rectangular (80) (1) (0.078) (640) I-19 Polymer 12 PAG 2TBA PGMEA 23.0 0.22 rectangular (80) (1) (0.078) (480) I-20 Polymer 12PAG 2 TBA PGMEA 22.0 0.20 rectangular (80) (1) (0.063) (480)

[0185] TABLE 2 Photoacid Dissolution Basic Optimum Base resin generatorregulator compound Solvent dose Resolution Example (pbw) (pbw) (pbw)(pbw) (pbw) (mJ/cm²) (μm) Shape I-21 Polymer 12 PAG 2 TMMEA PGMEA 22.00.20 rectangular (80) (1) (0.118) (480) I-22 Polymer 12 PAG 2 TMEMEAPGMEA 22.5 0.22 rectangular (80) (1) (0.173) (480) I-23 Polymer 7 PAG 2DRR 1 TEA PGMEA 22.0 0.24 rectangular (70) (1) (10) (0.063) (480) I-24Polymer s7 PAG 2 DRR 2 TEA PGMEA 23.5 0.22 rectangular (70) (1) (10)(0.063) (480) I-25 Polymer 7 PAG 2 DRR 3 TEA PGMEA 26.0 0.22 rectangular(70) (1) (10) (0.063) (480) I-26 Polymer 7 PAG 2 DRR 4 TEA PGMEA 24.50.20 rectangular (70) (1) (10) (0.063) (480) I-27 Polymer 7 PAG 2 ACC 1TEA PGMEA 23.0 0.22 rectangular (80) (1) (4) (0.063) (480) I-28 Polymer7 PAG 2 ACC 2 TEA PGMEA 24.0 0.22 rectangular (80) (1) (4) (0.063) (480)

[0186] TABLE 3 Compar- Photoacid Dissolution Basic Optimum ative Baseresin generator regulator compound Solvent dose Resolution Example (pbw)(pbw) (pbw) (pbw) (pbw) (mJ/cm²) (μm) Shape 1 Polymer 19 PAG 1 TEA PGMEA— — not (80) (1) (0.078) (480) resolved 2 Polymer 20 PAG 1 TEA PGMEA29.0 0.28 T-top (80) (1) (0.078) (480) 3 Polymer 19 PAG 1 DRR 4 TEAPGMEA 27.0 0.26 forward (70) (1) (10) (0.063) (480) tapered 4 Polymer 20PAG 1 DRR 4 TEA PGMEA 26.0 0.26 forward (70) (1) (10) (0.063) (480)tapered

[0187] It is seen from Tables 1 to 3 that the resist compositions withinthe scope of the invention have a high sensitivity and resolution uponKrF excimer laser exposure, as compared with prior art compositions.

Example II

[0188] Resist compositions were formulated using inventive polymers andexamined for resolution upon ArF excimer laser exposure.

Examples II-1 to II-2 Evaluation of Resist Resolution

[0189] Resist compositions were prepared as in Example I in accordancewith the formulation shown in Table 4.

[0190] The resulting resist solutions were spin-coated onto siliconwafers, then baked on a hot plate at 110° C. for 90 seconds to giveresist films having a thickness of 0.5 μm. The resist films were exposedusing an ArF excimer laser stepper (Nikon Corporation; NA 0.55), thenbaked (PEB) at 110° C. for 90 seconds, and developed with a solution of2.38% TMAH in water, thereby giving positive patterns.

[0191] The resulting resist patterns were evaluated as described below.First, the sensitivity (Eth, mJ/cm²) was determined. Next, the optimaldose (Eop, mJ/cm²) was defined as the dose which provides a 1:1resolution at the top and bottom of a 0.25 μm line-and-space pattern,and the resolution of the resist under evaluation was defined as theminimum line width (μm) of the lines and spaces that separated at thisdose. The shape of the resolved resist pattern was examined under ascanning electron microscope.

[0192] The composition and test results of the resist materials areshown in Table 4. TABLE 4 Photoacid Dissolution Basic Optimum Base resingenerator regulator compound Solvent dose Resolution Example (pbw) (pbw)(pbw) (pbw) (pbw) (mJ/cm²) (μm) Shape II-1 Polymer 1 PAG 1 TEA PGMEA17.0 0.16 rectangular (80) (1) (0.078) (480) II-2 Polymer 1 PAG 1 DRR 4TEA PGMEA 15.5 0.16 rectangular (70) (1) (10) (0.063) (480)

[0193] It is seen from Table 4 that the resist compositions within thescope of the invention have a high sensitivity and resolution upon ArFexcimer laser exposure.

[0194] Japanese Patent Application No. 2000-119410 is incorporatedherein by reference.

[0195] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. An ester compound of the following general formula (1):

wherein R¹ is hydrogen, methyl or CH₂CO₂R³, R² is hydrogen, methyl orCO₂R³, R³ is a straight, branched or cyclic alkyl group of 1 to 15carbon atoms, k is 0 or 1, Z is a divalent hydrocarbon group of 2 to 20carbon atoms which forms a single ring or bridged ring with the carbonatom and which may contain a hetero atom, m is 0 or 1, n is 0, 1, 2 or3, and 2m+n is 2 or
 3. 2. A polymer comprising recurring units of thefollowing general formula (1a-1) and/or (1a-2) derived from an estercompound of the general formula (1), and having a weight averagemolecular weight of 1,000 to 500,000,

wherein R¹, R², Z, k, m and n are as defined above.
 3. The polymer ofclaim 2 further comprising recurring units of at least one of thefollowing formulas (2a) to (10a):

wherein R¹, R² and k are as defined above, R⁴ is hydrogen or a carboxylor hydroxyl-containing monovalent hydrocarbon group of 1 to 15 carbonatoms, at least one of R⁵ to R⁸ is a carboxyl or hydroxyl-containingmonovalent hydrocarbon group of 1 to 15 carbon atoms, and the remaindersare independently hydrogen or a straight, branched or cyclic alkyl groupof 1 to 15 carbon atoms, or R⁵ to R⁸, taken together, may form a ring,and when they form a ring, at least one of R⁵ to R⁸ is a carboxyl orhydroxyl-containing divalent hydrocarbon group of 1 to 15 carbon atoms,and the remainders are independently a single bond or a straight,branched or cyclic alkylene group of 1 to 15 carbon atoms, R⁹ is amonovalent hydrocarbon group of 3 to 15 carbon atoms containing a —CO₂—partial structure, at least one of R¹⁰ to R¹³ is a monovalenthydrocarbon group of 2 to 15 carbon atoms containing a —CO₂— partialstructure, and the remainders are independently hydrogen or a straight,branched or cyclic alkyl group of 1 to 15 carbon atoms, or R¹⁰ to R¹³,taken together, may form a ring, and when they form a ring, at least oneof R¹⁰ to R¹³ is a divalent hydrocarbon group of 1 to 15 carbon atomscontaining a —CO₂— partial structure, and the remainders areindependently a single bond or a straight, branched or cyclic alkylenegroup of 1 to 15 carbon atoms, R¹⁴ is a polycyclic hydrocarbon group of7 to 15 carbon atoms or an alkyl group containing such a polycyclichydrocarbon group, R¹⁵ is an acid labile group, X is —CH₂— or —O—, and Yis —O— or —(NR¹⁶)- wherein R¹⁶ is hydrogen or a straight, branched orcyclic alkyl group of 1 to 15 carbon atoms.
 4. A method for preparing apolymer comprising the step of effecting radical polymerization, anionicpolymerization or coordination polymerization between an ester compoundof the general formula (1) and another compound having acarbon-to-carbon double bond.
 5. A resist composition comprising thepolymer of claim 2 or
 3. 6. A resist composition comprising the polymerof claim 2 or 3, a photoacid generator, and an organic solvent.
 7. Aprocess for forming a resist pattern comprising the steps of: applyingthe resist composition of claim 5 or 6 onto a substrate to form acoating, heat treating the coating and then exposing it to high-energyradiation or electron beams through a photo mask, and optionally heattreating the exposed coating and developing it with a developer.